1. Field of the Disclosure
The present subject matter relates to an umbilicus for use in a fluid processing system.
2. Description of Related Art
Whole blood is routinely separated into its various components, such as red blood cells, platelets, and plasma. In typical blood processing systems, whole blood is drawn from a donor, the particular blood component or constituent is removed and collected, and the remaining blood constituents are returned to the donor. By thus removing only particular constituents, less time is needed for the donor's body to return to normal, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for health care.
Whole blood is typically separated into its constituents through centrifugation. This requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the donor. To avoid contamination, the blood is usually contained within a sealed, sterile system during the entire centrifugation process. Typical blood processing systems thus include a permanent, reusable centrifuge assembly or “hardware” that spins and pumps the blood, and a disposable, sealed and sterile fluid processing or fluid circuit assembly that actually makes contact with the donor's blood. The centrifuge assembly engages and spins a portion of the fluid processing assembly (often called the centrifuge or separation chamber) during a collection procedure. The blood, however, makes actual contact only with the fluid processing assembly, which is used only once and then discarded.
To avoid the need for rotating seals, and to preserve the sterile and sealed integrity of the fluid processing assembly, blood processing systems often utilize centrifuges that operate on the “one-omega, two-omega” operating principle. This principle is disclosed in detail in U.S. Pat. No. 4,120,449 to Brown et al., which is hereby incorporated by reference, and enables centrifuges to spin a sealed, closed system without the need for rotating seals and without twisting the components of the system. Blood processing systems that make use of the principle typically include a fluid processing assembly that includes a plastic bag or molded chamber that is spun in the centrifuge and that is connected to the blood donor and to a stationary portion of the centrifuge assembly through an elongated member that may be made up of one or more plastic tubes. The elongated member is commonly referred to as an “umbilicus” and is typically arranged in a question mark (or upside-down question mark) configuration with both of its end portions coaxially aligned with the axis of rotation of the centrifuge. The centrifuge chamber is rotated at “two-omega” RPM and the umbilicus is orbited around the centrifuge chamber at “one-omega” RPM. In other words, one end of the umbilicus is stationary, the other end rotates at a two-omega speed with the centrifuge chamber to which it is attached, and the intermediate portion or midsection of the umbilicus orbits about the chamber at a one-omega speed. The effect is that the end of the umbilicus, which is opposite the bag or chamber and is connected to the donor via plastic tubing, does not twist up as the bag is spun. The sealed, sterile integrity of the fluid processing assembly is thus maintained without the need for rotating seals.
U.S. Pat. No. 5,996,634 to Dennehey et al., which is hereby incorporated herein by reference, discloses one such blood processing apparatus based on the “one-omega, two-omega” operating principle. In this apparatus, a disposable fluid processing assembly having an umbilicus and a processing chamber is mountable within a centrifuge assembly. One “fixed” end of the umbilicus is held rotationally stationary substantially over the axis of centrifugation. The other “free” end of the umbilicus joins the processing chamber and is free to rotate with the processing chamber around the axis of centrifugation. The mid-portion of the umbilicus is supported by a wing plate that orbits the mid-portion of the umbilicus around the axis of centrifugation at the one-omega speed. On account of having one “fixed” end and one “free” end, the umbilicus will “twist” about its own central axis as its mid-portion orbits around the processing chamber. The action of the umbilicus naturally “untwisting” itself will cause its “free” end (and, hence, the associated processing chamber) to spin at the average prescribed two-omega speed. This arrangement eliminates the need for complex gearing or belting arrangements to create a one-omega, two-omega drive relationship that was common in prior art devices. The umbilicus itself drives the processing chamber at a two-omega speed.
A typical umbilicus comprises a unitarily formed (generally by an extrusion process) main body defining a plurality of fluid-transmitting lumen. The body is formed of a material specially selected to perform the several required functions of the umbilicus, including being flexible enough to assume the proper orientation with regard to the centrifuge assembly, rigid enough to serve as a drive mechanism for rotating the processing chamber, and having a torsional stiffness leading to the aforementioned “untwisting” at the proper two-omega speed during fluid processing. A known material used in forming the umbilicus is the polyester elastomer material sold by E.I. DuPont de Nemours & Company under the trademark Hytrel®. While such a unitarily formed umbilicus has proven suitable, there can be difficulties in securing the umbilicus to the remainder of the disposable fluid processing assembly because of material differences or incompatibility. For example, it is common to employ polyvinyl chloride (“PVC”) tubing to connect at least one end of the umbilicus to other elements of the associated disposable fluid processing assembly. Thus, a PVC-to-Hytrel® material solvent bond is required to associate the umbilicus and the tubing. Additionally, an umbilicus comprised of Hytrel® material may be relatively expensive to manufacture. Accordingly, the need remains for a relatively low-cost improved umbilicus.